The present invention relates to a null monitoring system and more particularly to a null monitoring system for digital incremental scales.
It is desirable in any commercial weighing operation, but particularly in retail food operations, that strict accuracy and equity be maintained. Consumers are concerned that they receive full weight and value. Merchants wish to avoid embarrassment and possible prosecution for short weight but yet must be assured of full legitimate profit to survive. Analog weighing devices as heretofore used in the retail trade did provide through analog indices and means at least for virtual absolute zero resolution and definitive full range calibration. In recent digital devices without supplementary analog provision or other means, neither reference zero nor calibration over the weighing range can readily be resolved to less than plus or minus one-half of the minimum weight which is digitally indicated or recorded. Since net profit in retail operations today may sometimes not exceed one-half of 1%, a minus resolution error of that order may totally or substantially offset minimal and dissipated profits, or result in short weight publicity and prosecution. The monitoring system of the present invention heredisclosed is a novel and unique means for absolute resolution at zero and for the purpose of definitive calibration through the weighing range and yet permits the use of relatively inexpensive low-resolution encoders The monitoring system of the present invention is particularly valuable for use in conjunction with simple functional in-store check procedures insuring better than regulatory or common maintenance tolerances in use and as incorporated in several of assignee's present digital devices.
One form of digital scale utilizes a weighing platform and a reticle assembly including one or more light sources and light sensors and a displaceable reticle which is mechanically linked to the weighing platform for displacement proportional to the weighing platform displacement and ultimately to the weight of the load being weighed. Such reticles include light transmissive areas and opaque areas and cooperate with the light sources and light sensors to derive a plurality of counting pulses. When a load is placed onto the weighing platform, the scale weighing platform moves up and down in oscillating movement to cause the reticle assembly to provide the counting pulses. As the weighing platform moves in the down direction the counting pulses are added and as the weighing platform moves in the up direction the counting pulses are subtracted to ultimately obtain a net number of pulses when the weighing platform comes to rest.
Because the counting pulses are generated digitally, the position of the weighing platform can only be determined to within the least significant digit of the scale. For calibration purposes, it would be advantageous to determine the exact position of the weighing platform within the scale least significant digit.
It is therefore an object of the present invention to provide a null monitoring system for a digital scale for monitoring the exact position of the scale weighing platform within the scale least significant digit.
It is also an object of the present invention to provide a null monitoring system which generates an analog signal the magnitude of which is indicative of the scale weighing platform position within the scale least significant digit increment.
It is a still further object of the present invention to provide a null monitoring system which provides means for determining the exact position of the digital scale weighing platform within its least significant digit when the platform comes to rest.